This invention relates to a process for making a lithographic printing plate using an aluminum plate as a support and utilizing the silver complex diffusion transfer process.
Some examples of a lithographic printing plate using the silver complex diffusion transfer process (the DTR process) are described on pages 101 to 130 of Andre Rott and Edith Weyde, "Photographic Silver Halide Diffusion Processes", published by the Focal Press, London and New York (1972).
As described therein, there have been known two kinds of lithographic printing plates using the DTR process, i.e., a two sheet type in which a transfer material and an image-receiving material are separated and a mono-sheet type in which these materials are provided on one support. The two sheet type lithographic printing plate is described in detail in Japanese Provisional Patent Publication No. 158844/1982. Also, the mono-sheet type is described in detail in U.S. Pat. No. 3,728,114.
A mono-sheet type lithographic printing plate using an aluminum plate as a support and utilizing the silver complex diffusion transfer process (hereinafter referred to as "an aluminum lithographic printing plate"), which is the target of the present invention, is described in detail in Japanese Provisional Patent Publications No. 118244/1982, No. 158844/1982, No. 260491/1988, No. 116151/1991 and No. 282295/1992 and U.S. Pat. No. 4,567,131 and 5,427,889.
In the above aluminum lithographic printing plate, physical development nuclei are carried on a roughened and anodized aluminum support, and a silver halide emulsion layer is further provided thereon. A general process for making this lithographic printing plate comprises the steps of exposure, development processing, water washing processing (washing off: removal of a silver halide emulsion layer, hereinafter merely referred to as "washing processing") and finishing processing.
Specifically, metallic silver image portions are formed on physical development nuclei by development processing, and by washing processing subsequent thereto, a silver halide emulsion layer is removed to expose the metallic silver image portions (hereinafter referred to as "silver image portions") on an aluminum support. Simultaneously, the surface of anodized aluminum itself is exposed as non-image portions.
In order to protect the exposed silver image portions and non-image portions, a finishing solution containing a protective colloid such as gum arabic, dextrin, carboxymethyl cellulose and polystyrenesulfonic acid is coated thereon, i.e., said portions are subjected to the so-called gum coating processing. The finishing solution is also called as a fixing solution or a finisher and generally contains a compound which makes silver image portions oleophilic (hereinafter referred to as an oleophilic property-imparting agent).
As one of the problems of the above process for making an aluminum lithographic printing plate, there may be mentioned a problem that a water washing solution (hereinafter merely referred to as "washing solution") is made turbid. It has been found that such turbidity is caused by bringing a silver ion or a silver complex dissolved out in a developing solution into a washing solution. In the aluminum lithographic printing plate which is the target of the present invention, the efficiency of a silver complex trapped by physical development nuclei is lowered as compared with a conventional lithographic printing plate having physical development nuclei on a silver halide emulsion layer. Therefore, a large amount of a silver ion or a silver complex is dissolved out in a developing solution and brought into a washing solution.
As described above, washing processing is a step of removing a silver halide emulsion layer by peeling. Gelatin, chemically developed silver and so on which are peeled off from an aluminum support and dissolved or dispersed in a washing solution are recovered from the washing solution by a filter. The washing solution which has passed through the filter is generally circulated and used again. However, a silver ion or a silver complex cannot be recovered by the filter and makes the washing solution turbid. Further, there is an environmental problem in discharge of a treating liquid containing silver, and a measure to solve the problem has been demanded.
As other problems of the above process for making an aluminum lithographic printing plate, there may be mentioned a problem that the ink receptivity of silver image portions at the time of starting printing is low and a problem that printing endurance is insufficient. As a measure to solve the above problem of ink receptivity, it has been disclosed to incorporate an oleophilic property-imparting agent into a finishing solution in U.S. Pat. No. 5,436,110. Also, it has been described to incorporate an oleophilic property-imparting agent into a developing solution in the above publication. In U.S. Pat. No. 4,567,131, it has been disclosed to make a proteinase and an oleophilic property-imparting agent act in finishing processing.
By the above methods, ink receptivity has been improved to a certain extent. However, ink receptivity might be insufficient depending on change in printing conditions, for example, change in the kind of a printer, an ink or the like, and constantly stable and high ink receptivity has not yet been obtained. Therefore, further improvement has been demanded. With respect to the problem of printing endurance, desired property has not been obtained, and improvement of printing endurance has been demanded. Also, a conventional plate making process has a problem that ink receptivity is lowered with the lapse of time from plate making until printing.